Process for the manufacture of pour depressants for middle distillate fuels



Aprll 28, 1964 s. ILNCYKYJ ETAL 3,131,158

PROCESS FOR THE MANUFACTURE OF FOUR DEPRESSANTS FOR MIDDLE DISTILLATEFUELS Filed Jan. 5, 1960 Stephan \lnycxyj Joh Inventors y [L0 PatentAttorney United States latent O f 3,131,168 PROCESS FOR TE MANUFACTUREOF FOUR DEPRESSANTS FOR MID DLE DISTILLATE FUELS Stephan Ilneykyj andEehn L. Tiedie, Sarnia, Ontario, Canada, assignors to Esso Research andEngineering Company, a corporation of Delaware Filed Jan. 5, 1960, Ser.No. 593 1 Claim. (Cl. 260-873) The present invention is concerned withthe manufacture of improved pour depressants, particularly, for use withmiddle distillates. The pour depressant of the present inventioncomprises copolymers of ethylene with up to about 50% by weight of anolefinically unsaturated aliphatic monomer containing from about 3 to 5carbon atoms per molecule. The copolymers of a particular averagemolecular weight are obtained by controlling the conditions of reaction.The preferred copolymer of the present invention is a particularcopolymer of ethylene and vinyl acetate and is particularly directedtoward the method of manufacture wherein reagents are continuouslyadded.

With the increase in the use of hydrocarbon fuels of all kinds, aserious problem has arisen in areas frequently subjected to lowtemperatures in the cold test characteristics of fuels. Particularly,serious problems have been encountered with heating oils and diesel andjet fuels that have too high a pour point, resulting either indistributional or operating difficulties or both. For example, thedistribution of heating oils by pumping or syphoning is rendereddiificult or impossible at temperatures around or below the pour pointof the oil. Furthermore, the flow of the oil at such temperaturesthrough the filters cannot be maintained, leading to the failure of theequipment to operate.

Also the low temperature properties of petroleum distillate fuelsboiling in the range between about 250 and about 750 F. have attractedincreasing attention in recent years because of the growth of market forsuch fuels in subarctic areas and because of the development of turbojetaircraft capable of operating at altitudes where temperatures of -50 F.or lower may be encountered.

It is, therefore, an object of the present invention to set forth animproved process for the manufacture of very effective pour depressantsfor middle distillates and lighter oils. In general, these oils boil inthe range from about 250 to 750 F.

It is a still further object of the present invention to provide heatingoils, diesel fuel oils, kerosines and jet fuels having low pour points.Aviation turbo-jet fuels in which the polymers may be used normally boilbetween about 250 and about 550 F. and are used in both military andcivilian aircraft. Such fuels are more fully defined by US. MilitarySpecifications MIL-F-5 624C, MlL-F255 54A, MlI.-F-25558A, and amendmentsthereto. Kerosines and heating oils will normally have boiling rangesbetween about 300 and about 750 F. and are more fully described in ASTMSpecification D-396 4ST and supplements thereto, where they are referredto as No. 1 and No. 2 fuel oils. Diesel fuels in which the polymersmaybe employed are described in detail in ASTM Specification D-975-53T andlater versions of the same specification.

The process of the present invention produces copoly- 3,131,168 PatentedApr. 28, 1964 ice mers of ethylene and up to about 50% by weight of anolefinically unsaturated aliphatic monomer containing from about 3 to 5carbonatoms per molecule. In general, these compounds may comprise vinylacetate, vinyl propionate, methyl methacrylate, allyl ethyl ether,divinyl ether, acrylontrile, vinylacetonitrile and the like.

The preferred copolymers comprise ethylene-vinyl acetate copolymer. Itis preferred that the parts by weight of ethylene in the copolymer be inthe range from about 60 to 99% as compared to parts by weight of vinylacetate in the range from about 40 to about 1%. A very desirablepolyethylene vinyl acetate copolymer contains about 15 to 28% by weightof vinyl acetate, as for example, about 20 parts by weight of vinylacetate.

The molecular weights of the ethylene-vinyl acetate copolymer arecritical and should be in the range from about 1,000 to 3,000,preferably, in the range from about 1,500 to 2,200. The molecularweights are determined by K. Rasts method (Ber. 55, 1051, 3727 (1922)).

The ethylene-vinyl acetate copolymer as described above is used in aconcentration in the range from about .001 to 0.2% by weight,preferably, in a concentration in the range from about .005 to .l% byweight.

In accordance with the present invention, the polymerization process isconducted in a solvent as, for example, toluene or hexane. It ispreferred, however, to use a benzene solvent. The initiator comprisesany peroxy compound, preferably, di-tertiary-butyl-perordde. Thetemperature of the polymerization reaction is in the range from about280 to 340 F. A very desirable temperature is about 300 F. The pressureis in the range from about 700 to 2,000 pounds, preferably, 800 or 900pounds. The autoclave or similar equipment containing the solvent,initiator and vinyl acetate is purged with nitrogen, then with ethylenebefore charging with a sulficient amount of ethylene to yield thedesired pressure when heated to the reaction temperature. During thepolymerization, additional ethylene is added to maintain the pressure atthe desired level. Polymerization is considered complete when thepressure drops less than 50 p.s.i.g. per hour. The product is strippedfree of solvent and unreacted vinyl acetate under vacuum.

In accordance with the present invention, the reagents are continuouslyadded. A number of operations were carried out in order to establish theoptimum conditions for the manufacture of the pour depressant of thepresent invention.

In other operations, reactants were continuously fed to the reactor. Inthe first phase of this operation, vinyl acetate was charged into thereactor at the start of each run and di-tertiary-butyl-peroxide in 25%concentration in benzene was fed continuously as the copolymerizationproceeded. Table I compares products obtained with the best copolymer,A, produced when all reactants were charged to the reactor at thebeginning of the reaction.

The effect of reaction variables on yield and potency of pour depressantwas studied in some detail. Generally it was found that the yield ofcopolymer increased with polymerization time, slower rate of addition ofinitiator, and increases in pressure. In the range studied, the highestpotency pourdepressant was obtained when operating at 650 p.s.i.g. andusing short polymerization times with fast addition of peroxide. Whenconsidering both yield and quality of pour depressant, the best productwas obtained at 900 p.s.i.g., 300 F., 3 hours total polymerization timeand 1 hour addition time of peroxide.

TABLE I Operation A B O D E F G H I Reactor 1 2 Conditions:

Vinyl acetate, ml 30 150 150 150 150 120 120 120 90 Peroxide, ml 15 1515 15 15 15 15 Peroxide addition, hrs 0 4 1 1 1 1 1 1 1 Polymerization,hrs. 6 6 6 3 3 3 6 6 6 Pressure, p.s.i.g.. 850 900 900 3 1, 200 900 650650 650 550 Temperature, F 300 300 300 300 300 300 300 280 300 Product:

Yield, g 100 731 615 585 530 414 434 396 352 Initiator elficiency 61. 451. 7 49. 2 44. 5 34. 8 36. 5 33. 3 29. 5 Vinyl acetate, wt. percent 20.4 15. 8 20.6 18. 8 21.9 22. 8 21.0 21.9 20.9 Pour depressant, F.:

05 wt. percent 60 25 40 50 15 0.1 wt. percent 90 40 65 80 100 90 90 80Vinyl Acetate Balance:

Polymen'zed, wt. percent 72. 9 87. 5 90.6 78. 7 83.0 84.4 81.3 77. 5 87.4 Recovered monomer,

wt. percent 4. 9 8.2 7. 9 13.3 11.3 4. 7 7.6 Unaccounted for, wt.

percent 27. 1 7. 6 1.2 13.4 3. 7 4. 2 14.0 5.0

1 Litres. 2 One gallon. 3 Av.

Further improvements in the process were obtained when the vinyl acetatewas continuously added to the reactor as the polymerization reactionproceeded. These runs are shown in 'Table II.

TABLE 11 In general, the manufacture of the copolymer of the presentinvention is carried out at a temperature in the range from about 280 to340 F., prefenably at about 300 F. The pressure is in the range fromabout 700 to Pilot Copolymerization of Ethylene and Vinyl Acetate [Onegallon reactor, continuous addition of vinyl acetate and peroxide, 900p.s.i.g., 300 F.]

Operation A B O 1 D B E 2 F 2 G H 3 Conditions:

Benzene, ml 1,395 315 330 1, 395 345 405 1, 290 7, 740 Vinyl acetate,total 1111-. 150 150 150 150 150 150 300 1, 800 Vinyl acetate, at start,m1--- 150 30 16 150 0 0 0 0 Vinyl acetate, balance ml min 0 2.0 1. 1 02. 5 2. 5 5 15 Di-t-butylperoxide, tot 15 15 15 15 15 30 180Di-t-butylperoxide, mllm' 0.25 0.25 0.25 0.25 0.25 0.125 0. 25 1.0Polymerization time, hrs 3 3 6 3 3 3 3 3- 5 Product:

Yield, g 530 343 344 477 314 345 810 6, 700 Yield, g./g. peroxide 44. 528.9 28. 9 40. 0 26. 3 29. 0 v34. 0 46. 9 Vinyl acetate, Wt. percent.--21. 9 34. 0 33. 5 22. 7 27.6 31. 1 29. 8 23. 5 Pour depressant, F.: 4

0.05 wt. percent 60 55 45 50 35 75 80 90 0.1 wt. percent 80 70 90 90 8090 Vinyl acetate balance:

Polymerized, wt. percent--- 83. 6 83.4 82. 4 77.4 77. 4 77. 1 86. 2 93.9 Recovered monomer, Wt.

percent 13. 3 6. 0 8. 2 11.4 12. 4 11. 3 10. 5 Un accounted for, wt.percent 3. 7 10. 6 9. 4 11. 2 10.2 11. 6 3. 8 6. 1

1 800 p.s.i.g.

1 Inhibitor removed from vinyl acetate.

3 5 U.S. gallons reactor.

4 50/50 blend of virgin and cat. cracked gas oils, pour +20 F.

The advantages of these operations were improved quality of pourdepressant and substantially reduced solvent requirement. This latterfactor resulted not only in a reduction of solvent required, but also inmuch higher utilization of reactor volume. See Table III.

TABLE III Synthesis of Pour Depressants 50/50 blend of virgin gas oiland cat. cracked gas oil, ASTM pour +20 F.

,is first purged with nitrogen, introduced by means of line, 7'

12 and pump 13. Reactor 20 is then purged ethylene which is introducedby means of line 12 and pumplfl. Gases are removed from reactor 20 bymeans of line 11 The reactor is maintained at a positive pressure in therange from about 50 to pounds absolute.

Approximately 220 parts by Weight of benzene is introduced into reactor:20 from benzene storage 1 by means of dine 6 and pump 5. .Reactor 20 isthen raised to a temperature of 300 F. by means of heating element 14wherein a heating fluid or equivalent is introduced by means of line '15[and withdrawn by means of line 16. Reactor 20 is held at 300 F. duringthe course of the reaction by the removal of heat or by the addition ofheat thereto. Ethylene is introduced by means of line 12 so as to raisethe pressure of the reactor to about 900 pounds.

The addition of vinyl acetate and of di-tertiary-butylperoxide isstarted concurrently. The vinyl acetate is withdrawn from storage zone 3and introduced into the reactor by means of line and pump 9.Approximately 55 parts by weight of vinyl acetate is added over a twohour period. The peroxide is introduced by passing benzene into storagezone 2 by means of line 4 and then introducing the solution into thereactor '20 by means of line 8 and pump 7. Approximately 5.5 parts byweight of peroxide are combined with 16.5 parts by Weight of benzene.The resulting 22 parts by weight of 25% peroxide solution in benzene isadded to reactor 20 over a three hour period.

After the addition of the peroxide has been completed, the reactor isheld for an additional one-half hour at a temperature of about 300 Theethylene is added continuousiy so as to maintain the pressure at about900 pounds. in operation, approximately 934 parts by weight or vinylacetate are used in conjunction with from about 2,800 to 3,800 parts byweight of ethylene.

At the end of the reaction, the reactor is allowed to cool to about 160F. and the reaction product is then withdrawn by means of line 17 andpassed into separation zone 18. Excess ethylene is removed overhead fromseparation zone 13 by means of line 19. The polymer product comprisingthe copolymer in a benzene solution may be withdrawn by means of line 22and further handled as desired. Under certain instances, it may bedesirable to separate at least a portion of the benzene from thecopolymer. Under these conditions, the henzene copolymer product ispassed to separation zone 30 by means of line 21. Benzene is removedoverhead by means of line 24, while a copolymer product is with drawn bymeans of line 23.

The quantity mentioned above may be somewhat varied. For example, basedupon 55 parts by weight of vinyl acetate, the amount of benzene utilizedmay vary from about 180 to 300 parts by weight, and the amount ofditertiary-butyl-peroxide may vary from about 3 to 8 parts by weight.Also as mentioned, the amount of ethylene utilized varies from about2,800 to 3,800 parts by weight, or approximately 938 parts by weight ofvinyl acetate. T 13 time of reaction also may be varied from about 2 to4 hours, depending upon other operating variables.

While the above operation has been described utilizing a single reactor,it is to be understood that a plurality of reactors may be employed in asimilar manner in order to secure continuous production of thecopolymer.

What is claimed is:

Process for the manufacture of a pour depressant consisting essentiallyof a copolymer of ethylene and vinyl acetate, which copolymer has amolecular weight in the range from about 1500 to 2200 as determined byRasts method, and is characterized by containing from about 15 to 28% byweight of vinyl acetate which comprises purging a reaction zone withnitrogen and thereafter introducing about 220 parts by weight of benzeneinto a reaction zone, heating the benzene to a temperature of about 300F., thereafter pressuring said reaction Zone with ethylene to about 900pounds, thereafter continuously adding about parts by Weight of vinylacetate over a reaction time period of about two hours and alsocontinuously adding over a reaction time period of about three hoursabout 22 parts by weight of a benzene solution containing about 25% byweight of di-tertiary-butylperoxide while maintaining said reaction zoneat the conditions specified to produce said copolymer, whereby about 310parts by weight to 142 parts by weight of ethylene will react with said55 parts by weight of vinyl acetate.

References Cited in the file of this patent UNITED STATES PATENTS2,396,785 Hanford Mar. 19, 1946 2,414,311 Larson Ian. 14, 1947 2,450,451Schmerling Oct. 5, 1948 2,551,643 Seger et a1 May 8, 1951 FOREIGNPATENTS 459,662 Canada Sept. 13, 1949

